The present invention relates to orthopedic implants and to methods of treating bone defects. More specifically, but not exclusively, the present invention is directed to non-metallic orthopedic implants, methods for intra-operative assembly of the orthopedic implants, and methods of internal fixation of bone tissue to facilitate medical treatment.
It is known to use orthopedic implants, such as plates, rods, and screws, to repair and treat bone defects, such as cracked and broken bones, and disorders of the musculoskeletal system. In the past, many of the orthopedic implants were formed primarily of metallic materials. The metallic implants offer many advantages. They can be readily sterilized, are biocompatible, and provide the requisite strength for support and/or fixation of the bony tissue. However, metallic implants also exhibit a significantly greater compressive modulus over cortical bone. The metallic implant can stress-shield new bone growth to induce osteoporosis and/or osteopenia, resulting in cortical bone that is prone to refracture. After the bone defect was repaired, often the implants were no longer needed to maintain the patient's mobility. While some metal implants were allowed to remain in place, many were removed. Their removal required a second surgical procedure. Obviously, it would be more desirable to eliminate the second surgical procedure to minimize patient pain/discomfort, chance of infection, and subsequent trauma to the newly healed site, while at the same time removing the implant as a potential source of irritation for surrounding tissue.
More recently, new treatment methods and improved materials, including non-metallic implants, have been used to treat bone defects. The non-metallic implants can remain in the body, or alternatively, selected implants can be made of materials that biodegrade over a time period ranging from a few days to several months.
While the new materials have provided significant advances over the previous medical devices, there still remain significant problems requiring continued development for non-metallic medical implants—not the least of which is their lower mechanical strength compared with their metallic counterparts. Typically, non-metallic orthopedic implants have not provided sufficient strength to be used alone for internal fixation of load-supporting bone tissue, such as the long bones of the upper and lower limbs and the spine. Further, selected non-metallic implants such as bone plates can fail when installed with non-metallic bone fasteners. Reduced friction between contacting surfaces of fastener and bone plate; lower mechanical strength; lower holding force; and in selected materials, biodegradation of the implants themselves, to name a few examples, all can contribute to an unacceptable failure rate for the non-metallic implants. Even metallic fasteners have been known to dislodge or back out from the implant and/or bone tissue. The non-metallic fasteners can be even more prone to dislodge. The non-metallic fasteners cannot be tightened or torqued sufficiently to prevent the fastener from disengaging from the plate. The non-metallic bone screws do not exhibit the mechanical strength of metal counterparts, and typical mechanical lock mechanisms and techniques often fail to maintain an integral connection with non-metallic fasteners—requiring revision surgery. This can be acerbated for implants formed from biodegradable materials, which successively degrade over time and which become increasingly weaker as they degrade. These are but a few of the problems faced by patients and their physicians in selecting an appropriate course of treatment.
In light of the above-described problems, there is a continuing need for advancements in the relevant field, including improved methods, compositions, and devices to provide non-metallic implants that exhibit a high rate of successful orthopedic and musculoskeletal treatment and yet reduce necessity for subsequent surgical intervention. The present invention is such an advancement and provides a wide variety of benefits and advantages.